Though the chain's char-broiled Atlantic cod sandwich might seem like a no-brainer, the industry has favored the fryer since the 1960s when the Golden Arches introduced the Filet O' Fish.

More surprising is that of all chains to roll out a fish sandwich perceived as more healthful than its fried brethren, it's Hardee's and sibling Carl's Jr. The latter has long been known for big, indulgent burgers and sexy ads featuring women like Kim Kardashian and Paris Hilton that appeal to young men.

"Rather than just do the same thing, we took advantage of our unique selling proposition, which is [the] char-broiled burger, and developed this" to offer a lower-calorie option, said Brad Haley, chief marketing officer for Carl's Jr. and Hardee's.

It's reasonable to think that the limited-time sandwich would appeal more to women. But the ad for the product, featuring model Nina Agdal in a bikini, seems to do anything but. However, Mr. Haley said the commercial attracts men because it features a woman in a swimsuit, but will be relevant to women who will connect the dots between Ms. Agdal eating a char-broiled sandwich and having a bikini-ready body.